Field of the Invention
The invention relates to a method for fabricating a microelectronic component, in which a storage capacitor is formed on a substrate. A barrier, which affords protection against the passage of hydrogen is formed on the storage capacitor. The invention furthermore relates to a microelectronic component of this type.
Conventional microelectronic semiconductor memory components (DRAMs) essentially include a selection or switching transistor and a storage capacitor in which a dielectric material is inserted between two capacitor plates. Oxide or nitride layers having a relative permittivity of at most about are usually mostly used as a dielectric. In order to reduce the size of the storage capacitor and in order to fabricate non-volatile memories, xe2x80x9cnovelxe2x80x9d capacitor materials (ferroelectrics or paraelectrics) with significantly higher relative permitivities are required. Examples of such materials are mentioned in the publication xe2x80x9cNeue Dielektrika fxc3xcr Gbit-Speicherchipsxe2x80x9d [New dielectrics for Gbit memory chips] by W. Hxc3x6nlein, Phys. Bl. 55 (1999). In order to fabricate ferroelectric capacitors for use in non-volatile semiconductor memory components having a high integration density, it is possible to use e.g. ferroelectric materials, such as SrBi2(Ta,Nb)2O9 (SBT or SBTN), Pb(Zr,Ti)O3 (PZT), or Bi4Ti3C12 (BTO) as a dielectric between the capacitor plates. However, it is also possible to use a paraelectric material, such as (Ba,Sr)TiO3 (BST), for example.
However, the use of these novel dielectrics presents the semiconductor process technology with new challenges. This is because, firstly, these novel materials can no longer be combined with polycrystalline silicon, the traditional electrode material. Therefore, it is necessary to use inert electrode materials such as, for example, platinum-group metals or their conductive oxides (e.g. RuO2). The reason for this is that after the deposition of the ferroelectric, the latter has to be subjected to heat treatment (xe2x80x9cconditionedxe2x80x9d) if appropriate a number of times in an oxygen-containing atmosphere at temperatures of about 550-800xc2x0 C. In order to avoid undesirable chemical reactions between the ferroelectric and the electrodes, the latter are therefore mainly produced from platinum or another sufficiently thermostable and inert material, such as another platinum-group metal (Pd, Ir, Rh, Ru, Os).
For the integration of the storage capacitors, process steps are performed which take place in a hydrogen-containing environment. Thus, by way of example, the conditioning of the metallization and of the transistors requires a heat treatment in forming gas, which has a composition of 95% nitrogen (N2) and 5% hydrogen (H2). The penetration of hydrogen into the processed storage capacitor, i.e. into the dielectric, can, however, lead to degradation of the oxidic ceramics of the dielectric as a result of reduction reactions. Furthermore, the plasma-enhanced deposition (PECVD) of intermetal oxides or of the silicon nitride passivation layer can, on account of the high hydrogen content in the layers, cause reduction of the ferroelectric or paraelectric material of the dielectric. Hydrogen also appears during the deposition of electrically conductive materials, for instance refractory metals such as tungsten or titanium. The deposition serves, for example, to produce layers or to fill contact holes.
Furthermore, the penetration of hydrogen into the storage capacitor also adversely affects the structural properties. Thus, a peeling effect, for example, can occur.
It is already known to apply a silicon nitride layer to the storage capacitor as a barrier against the penetration of hydrogen. Silicon nitride is deposited, for example, according to the LPCVD (Low Pressure Chemical Vapor Deposition) process at about 750xc2x0 C. The starting materials in the formation of silicon nitride are SiH2Cl2 and NH3. During the deposition, however, hydrogen radicals are formed and the storage capacitor is thus damaged.
Furthermore, it is known to form hydrogen barriers made of materials, which can be deposited without hydrogen being present. Examples of such materials are AlOx, TiOx, TiOxNy. However, these oxidic materials are difficult to etch, with the result that, after the customary silicon oxide layer has been applied to the barrier, contact holes to the electrodes of the storage capacitors and/or through the barrier to the substrate material can be etched only in conjunction with a high outlay.
It has also already been proposed to omit the filling of contact holes with tungsten, which is done in the presence of hydrogen, and to use aluminum instead. Contemporary commercially available products with ferroelectric dielectrics are therefore embodied with aluminum as metallization material. However, a region to be filled can be filled significantly more reliably with tungsten than with aluminum. In any event, contemporary known methods for filling with aluminum must be dispensed with in the course of further miniaturization and further increasing of the storage densities of semiconductor memories.
It is accordingly an object of the invention to provide a microelectronic component and a method of producing a microelectronic component which overcome the above-mentioned disadvantages of the heretofore-known methods and components of this general type and which allow contact holes to be etched in a simple manner after the application of an effective hydrogen barrier. At the same time, there should not be any considerable damage to the storage capacitor as a result of the application of the hydrogen barrier.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating a microelectronic component, the method includes the steps of:
forming a storage capacitor on a substrate by providing a first electrode and a second electrode and by providing a dielectric selected from the group consisting of a ferroelectric dielectric and a paraelectric dielectric disposed between the first electrode and the second electrode; and
forming a barrier by producing a silicon oxide layer on the storage capacitor, by subjecting the storage capacitor and at least part of the silicon oxide layer to a heat treatment, and by applying a barrier layer on the silicon oxide layer for protecting against a passage of hydrogen through the barrier.
An essential concept in the method according to the invention is that, during the barrier formation, firstly a silicon oxide layer is produced. The storage capacitor and at least part of the silicon oxide layer are subjected to heat treatment, i.e. are thermally treated in particular immediately after the deposition of the silicon oxide layer. By way of example, the storage capacitor and the silicon oxide layer are baked at a temperature of 500xc2x0 C. or higher, preferably 650xc2x0 C. or higher, in an oxygen atmosphere.
A barrier layer, which affords protection against the passage of hydrogen is applied to the heat-treated silicon oxide layer.
In particular if the electrodes of the storage capacitor contain platinum or a platinum-group metal, the silicon oxide layer takes from the platinum or platinum-group metal the catalytic activity, i.e. drastically reduces or substantially eliminates the catalytic activity, which, in the presence of hydrogen, can lead to particularly severe damage to the storage capacitor. Therefore, subsequent process steps in which hydrogen is present lead only to slight or even no damage to the storage capacitor. Therefore, the silicon oxide layer is preferably applied directly to the electrode material.
The heat treatment or the baking of the storage capacitor and at least part of the silicon oxide layer has the effect that hydrogen which, during the application of the silicon oxide layer, has penetrated into the vicinity of the storage capacitor or has penetrated into the latter is removed again. The heat treatment advantageously takes place in an oxygen-containing atmosphere, so that the oxygen bonds with the hydrogen (water molecule formation). The heat treatment already leads to the required conditioning of the dielectric before the application of the hydrogen barrier layer.
Preferably, at least part of the silicon oxide layer is deposited in a low temperature process, in particular a PECVD (Plasma Enhanced Chemical Vapor Deposition) process. In this case, the temperature is about 350xc2x0 C., for example. An essential advantage of the low temperature process is that the hydrogen present does not lead to permanent damage to the storage capacitor. As a result of the subsequent heat treatment, preferably at significantly higher temperatures, penetration of hydrogen into the storage capacitor is reversible. Moreover, at the low temperature, the chemical reactions between the hydrogen and the dielectric material, which can proceed at high temperatures do not take place.
The silicon oxide layer is generally densified by the heat treatment, in particular if the heat treatment is effected at a higher temperature than the deposition. This already provides a partial protection against the passage of hydrogen.
Finally, the heat treatment of the silicon oxide layer has a favorable effect on its behavior during the further method steps, since the silicon oxide layer is already exposed, during the heat treatment, to the temperatures, which generally lead to a structural change. Such structural changes are undesirable, for example, during the subsequent application of the barrier layer because they can have an unfavorable effect on the structure and the adhesion behavior of the barrier layer. The same applies correspondingly to materials that are subsequently applied to the barrier layer, for instance an insulation layer, which embeds the storage capacitor and the barrier.
Preferably, a partial layer of the silicon oxide layer which is applied to a partial layer that has already been applied is deposited in a high temperature process, in particular an HTO (High Temperature Oxide) process. On account of the high temperature, it is possible to produce silicon oxide with a high density without subsequent heat treatment of the partial layer. Nevertheless, it is preferred also to carry out a heat treatment after the application of this partial layer, in order to anneal any damage due to penetrated hydrogen of the storage capacitor and/or to bake out penetrated hydrogen.
The invention makes it possible to use tungsten for electrical contact-connection, in particular for filling contact holes, which are introduced into the abovementioned insulation layer and the barrier, since the capacitor can be effectively protected against penetration of hydrogen by the barrier. Consequently, further miniaturization is possible and higher storage densities can be achieved in microelectronic memory modules.
Preferably, at least part of the barrier layer is applied to the heat-treated silicon oxide layer in a hydrogen-free deposition process. In this case, the thickness of the part of the barrier layer can be kept so small that, in the case of materials that are inherently difficult to etch, such as metal oxides, the barrier layer can be etched with a tenable outlay. If such a partial layer of the barrier layer is applied, then a further partial layer can be applied in the presence of hydrogen, since the previously applied part of the barrier layer already protects the storage capacitor from the hydrogen.
If at least parts of the barrier layer are applied or deposited in the presence of hydrogen, then a heat treatment of the storage capacitor, of the silicon oxide layer and of the already applied part of the barrier layer is preferably carried out afterward. What is applicable to the heat treatment before the application of the barrier layer is correspondingly applicable to this.
In a preferred embodiment, a partial layer of the barrier layer, which, however, is not the partial layer applied first, is composed of silicon nitride or a silicon nitride layer is applied. In this case, the previously applied at least one partial layer of the barrier layer acts as a buffer for the hydrogen which is present during the application of the silicon nitride layer. Depending on the material of the previously applied partial layer, the latter is a barrier and/or a store for hydrogen. Examples of materials, which store hydrogen are titanium and most of its compounds.
Suitable materials for the barrier layer are, in particular, Ti, TiN, TiOx (for example reactively sputtered or oxidized from Ti at e.g. 700xc2x0 C., for 5 minutes in an oxygen atmosphere), Ta, TaN, TaOx (e.g. reactively sputtered or oxidized from Ta at e.g. 700xc2x0 C., for 5 minutes in an oxygen atmosphere), AlOx, NbOx, ZrOx and/or SixNy.
In particular, a barrier layer or partial layer made of SixNy can be deposited in an LPCVD (Low Pressure Chemical Vapor Deposition) process at about 600-750xc2x0 C., preferably 660xc2x0 C., and a pressure of 30 Pa. Furthermore, an SixNy layer can be deposited in an LP (Low Pressure) microwave process in which at least one SixNy precursor is activated by microwave radiation. In this way, it is possible to avoid the NH3, which is present in the LPCVD process and is a starting material for the formation of hydrogen.
The SiN layer can also be fabricated by sputtering, thereby likewise avoiding the occurrence of H2 during the deposition.
By forming the silicon oxide layer in the form of two or more than two partial layers, the partial layers being applied in different fabrication processes and therefore having a different oxide structure, it is possible, as described above, largely to avoid damage to the storage capacitor. As a result, moreover, it is possible to form a good foundation for applying the actual barrier layer and to reduce the catalytic effect of platinum or platinum-group metal present in an outer electrode of the storage capacitor.
With the objects of the invention in view there is also provided, a microelectronic component, including:
a substrate;
a storage capacitor formed on the substrate;
the storage capacitor including a first electrode, a second electrode and a dielectric selected from the group consisting of a ferroelectric dielectric and a paraelectric dielectric, the dielectric being disposed between the first electrode and the second electrode; and
a barrier including a silicon oxide layer and a barrier layer, the silicon oxide layer being disposed on one of the first and second electrodes and having been subjected to a heat treatment in an oxygen-containing atmosphere, the barrier layer being disposed on the silicon oxide layer and protecting the storage capacitor against a passage of hydrogen through the barrier.
The barrier layer preferably has two partial layers made of different material. In particular, the partial layer located nearer the silicon oxide layer is made of a metal-oxide-containing material and has a layer thickness of 50 nm or less, preferably approximately 20 nm. Appropriate metals for the metal oxides are, in addition to the metals already mentioned, all transition metals. As an alternative, nitrides of the transition metals are appropriate as material for a partial layer of the barrier layer or for the barrier layer in its entirety. In particular, the partial layer located further away from the silicon oxide layer is a silicon nitride layer preferably having a layer thickness of approximately 25 nm.
According to another feature of the invention, an insulation layer is disposed on the barrier such that the storage capacitor and the barrier are embedded in the insulation layer.
According to yet another feature of the invention, the insulation layer has a contact hole formed therein, and a tungsten contact fills the contact hole and electrically contacts one of the first and second electrodes.
According to a further feature of the invention, the silicon oxide layer has two heat-treated partial layers with different oxide structures.
According to another feature of the invention, the barrier layer has two partial layers made of different materials.
According to yet another feature of the invention, a first one of the two partial layers is located closer to the silicon oxide layer than a second one of the two partial layers, and the first one of the two partial layers is composed of a metal-oxide-containing material and has a layer thickness of at most 50 nm, preferably of substantially 20 nm.
According to another feature of the invention, a second one of the two partial layers is located further away from the silicon oxide layer than a first one of the two partial layers, and the second one of the two partial layers is a silicon nitride layer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a microelectronic component and a method for fabricating a microelectronic component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.